This invention relates to the recycling of petroleum-based wax coated or impregnated waste paper and more particularly to the recycling of old corrugated cartons (OCC) which have been impregnated or coated with conventional petroleum-based wax.
Wax saturated and wax coated cartons are particularly useful for shipping and storing food and produce, such as iced fresh produce, seafood, poultry and refrigerated meats. It is also useful as industrial packaging where a product is exposed to water and/or very high humidities and to packaging which require high stacking strengths and stiffness under dry conditions.
The waxes which are most commonly used comply with U.S. Federal Drug Administration requirements and regulations for use as an indirect food additive and as a component of paperboard in contact with food products. Saturating waxes have also been approved by the United States Department of Agriculture (USDA) for use in packaging of meat, fish, and poultry under federal inspection, and are approved for packaging materials which come into direct contact with such poultry or food products. Such waxes are relatively easy to deploy since application temperatures run in the range of about 190-210.degree. F., depending on the particular wax grade and the product, and have relatively low melting points in the range of about 125-140.degree. , depending upon the wax formulation.
The same moisture resistant characteristic of such carton material has formed an impediment to satisfactory use of repulped petroleum-based waxed paper products. Wax corrugated material or board packaging material is not generally considered to be an accepted source of secondary fiber. Small undispersed particles of wax can form dark spots on a sheet, often referred to as a wax spot, thereby providing an undesirable blemish. More importantly, only a small percentage of wax mixed within the cellulose fibers drastically reduces both the strength and the dry coefficient of friction, measured as a slide angle, of the finished carton product. A small percentage of residual wax in the furnish can reduce the coefficient of friction and the slide angle to the point where the resulting carton material is not acceptable. Existing OCC reclaiming systems, in most up-to-date paper and pulp mills, are state-of-the-art systems and function well on a furnish of traditional OCC. The introduction of varying amounts of wax material into such existing systems tends to upset that process, and contaminates the entire system.
Also, a small amount of wax saturated OCC by volume or by weight, can add a significant amount of wax to mixed OCC and to a recycled paperboard furnish. Therefore, it is often necessary, in recycling, manually or by other means to separate out the heavily waxed cartons, to prevent an overloading of wax in the furnish. The principal obstacles to recycling waxed OCC is the resulting low paper-to-paper friction for packaging papers, the negative effect on strength, and generally reduced quality of the recycled product. Although cascade coated wax board products are beneficial and provide desirable moisture barrier and food compatible qualities at low costs, nevertheless this product carries with it the stigma that it is not considered to be recyclable, using presently known techniques.
While petroleum wax coated or impregnated OCC represents approximately 5% of the U.S. production of corrugated carton material, only a small portion of this can be recycled and reclaimed, and then must be mixed with a very substantial portion of unwaxed OCC. Considerable efforts have been expended to improve the recyclability of petroleum waxed packaging products and improve the related processes. A major stumbling block has been the finding by leading researchers that waxed paper was not repulpable in a conventional hydra pulper. McEwen and Wang "OCC Recycling: Improving The Repulpability Of Wax Coated Corrugated Paperboard" Tappi 1992 Pulping Conference Book 2, Nov. 1-15, 1992, pages 493-502 concluded that waxed corrugated carton is not an acceptable source of secondary fiber and that commercially available carton coatings (wax) are considered non-repulpable. In repulpability tests, the pulper was operated at a temperature below the melting point of the wax, for the purpose of allowing the wax to remain in pieces, for subsequent screening and cleaning. When the temperature in the pulper was raised from 49.degree. C. to 68.degree. C., close to the wax melting point, the paper became defibered but most of the wax softened and deposited on the pulper surface, an unsatisfactory result. McEwen and Wang went on then to test the effect of adding chemicals to the wax prior to the wax being applied for the purpose of promoting the release of the wax component, in repulping, of the paper fibers from the wax in order to maintain pulping temperatures far below the wax melting point.
Back and Jousimaa, "Wax Removal After Alkaline Hot Dispersion On A Pilot Plant Scale, Autodispersible Waxes For Recyclable Packaging Of Papers," Progress in Paper Recycling, November 1955, pages 91-99, describe the results of using a wax coating which has been previously specially modified with fatty acids to facilitate subsequent removal from OCC. Pulping was accomplished in a chest at a temperature well below the congealing temperature of the wax, and hot dispersion was accomplished in a separate disk refiner at a pH of about 11.0 with wax removal taking place in one or more dewatering screws. Removal of such pre-treated wax using a low pitch screw press was observed as high as 90%. No data is given on the removal of unmodified petroleum waxes.
Galland, Vernac, and Brun, "Recycling Of Wax Papers & Boards," Tappi, Mar. 5-7, 1996, Tappi Recycling Symposium, pages 81-89 describes experimental efforts to remove conventional untreated wax from OCC. The wax coated paper was repulped at low temperature to avoid deposition of wax in the pulper pipes and chests. Subsequently, wax dispersion was accomplished in a separate kneader, and conventional screening was attempted to remove the wax. After two screening passes the total efficiency did not exceed 86%, and the 21/2% residual wax was considered as rendering the combination inefficient. Flotation using deinking flotation cells provided a higher efficiency of nearly 95%. Flotation appeared to be the most appropriate technique to remove wax although the flotation cell induced an additional loss of 15 to 20% of the pulp. This reject rate appeared to the authors to be too high for papermakers to economically produce corrugated paper.
There accordingly exists a long felt need to provide a method and system by which unmodified wax content of waxed OCC or by which an excessive was content of a furnish may be efficiently and effectively removed or reduced, without wax buildup in the tanks and pipes, without unacceptable degradation of the pulp, with acceptable losses, to produce a dewaxed paper pulp having a wax content of 1% or less. There is likewise a need for an efficient process for pretreating a waxed furnish so that it may be introduced without detriment into an existing OCC system.